A steering-by-wire method has been gradually deployed in a boat as a boat operating system. This method mainly uses a motor pump and relies on hydraulic control thereof.
On the other hand, in order to improve operationality of leaving and getting to the shore, it is suggested to equip a boat with two or more propulsion devices and to control behavior of the boat by output control and rudder angle control of each thereof (for example, see Patent Literature 1).